The present invention relates to a permanent magnet dynamo electric machine and, in particular, to a permanent magnet dynamo electric machine having embedded permanent magnets inside the rotor thereof.
There are two types of conventional permanent magnet dynamo electric machines, In, in one type, the permanent magnets are secured on the circumference of the rotor thereof, and in the other type the permanent magnets are embedded inside the rotor thereof. JP-A-5-76146 (1993) discloses a structure of the latter type.
In the permanent magnet dynamo electric machine having a structure of the latter type, when the rotor thereof is rotating, centrifugal forces acting on the respective permanent magnets are applied to portion of the rotor members located along the outer circumferences of the respective permanent magnets. Further, the rotor members themselves are subjected to centrifugal forces. Portion which are located at both circumferential ends of the rotor members, namely the bridge portions, support the above mentioned two sorts of centrifugal forces. Therefore, in order to withstand centrifugal forces caused by high speed rotation, the thickness of the bridge portions has to be increased.
On the other hand, when the thickness of the bridge portions is increased, magnetic fluxes generated by the permanent magnets leak via the bridge portions to the surrounding iron core, and the amount of magnetic fluxes transferred from the surface of the rotor to the stator thereof is decreased. Torque generated by the permanent magnet dynamo electric machine depends on the amount of magnetic fluxes transferred from the permanent magnets the stator, therefore, if the magnetic flux leakage increases, the torque generated decreases and the efficiency of the permanent magnet dymano electric machine is reduced accordingly.
An object of the present invention is to provide a permanent magnet dynamo electric machine having embedded permanent magnets inside the rotor thereof which permits high speed rotation and enhances the efficiency thereof, by suppressing the magnetic flux leakage via, the bridge portions"" while limiting the loading due to centrifugal forces applied to the bridge portions.
The object of the present invention is achieved by a permanent magnet dynamo electric machine comprising a stator having a stator iron core in which a stator winding is wound, and a rotor facing the inner circumference of the stator and rotatably supported thereby, the rotor being constituted by a columnar rotor iron core, a shaft provided along the rotation axis of the rotor iron core and a plurality of permanent magnets arranged in a ring along the circumference of the rotor iron core so as to face the stator iron core, characterized in that, the rotor iron core is provided with the same number of permanent magnet insertion holes as the number of permanent magnets for receiving the same at positions the ratio R1/R0 is equal to or more than 0.85, wherein R0 is the radius of the rotor and R1 is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets at the side remote from the stator.